Handbook to the Primates/Lemuroidea

The Aye-Aye, the Tarsier, and the True Lemurs constitute this first sub-order. They are characterised by having the muzzle long and narrow, more or less Dog-like in shape, and the upper lip often divided into two by the nose-pad. The external ears (Fig. 1) are enlarged, with flattened margins, but have no "hem" as in the higher Anthropoids. (Fig. 2.)

The trunk is relatively long and compressed, and the tail when long is never truly prehensile. Of the limbs, the posterior are longer than the anterior, and all have five digits, each bearing a flat nail except the second toe, which has invariably a long pointed claw, their tips ending in prominent discoidal tactile pads. (Fig. 3.)

Of the digits, the index is sometimes quite rudimentary, while the thumb is large, and the great toe especially so, both being opposable. Teats occur on the breast, on the abdomen, or on both.

Of the skeleton, the eye-sockets, or orbits, are directed forward, and have complete bony margins, which, however, are not closed in by bone behind (as in Monkeys), but freely communicating beneath the post-orbital process (except in Tarsius) with the temporal hollow behind. In the young of some species the orbit is more enclosed than it is in the adult: the orifice for the lachrymal duct of the eye is placed external to the margin of the orbit: the hollow for the olfactory lobes of the brain is always large.



Having four kinds of teeth, and a set in succession to the milk-teeth, they are Heterodont and Diphyodont. The dental formula is I $2⁄2$, C $1⁄1$, P $3⁄3$, M $3⁄3$ = 36 (vide anteà, p. 6), and the upper jaw has a toothless space in the centre (except in the Aye-Aye). Of the upper teeth, the incisors are sometimes absent, but generally present; if unequal in size the inner one is the larger of the two. The canines are prominent; the pre-molars all have a cingulum, or girdle, round the base, more or less enlarged backwards into a process ("talon" or "heel"); the anterior pre-molar vertically long and canine-shaped; the median and posterior with three main points (tubercles or cusps) and one or two smaller ones on the crown, and having a bar or ridge uniting the front inner with the hind outer cusp. The anterior and median molars have three or four main cusps, and one or two smaller or subsidiary ones on the crown; the cingulum is well developed. The posterior molars have generally three cusps.

In the lower jaw the incisors are close-set and comb-like, remarkable for protruding in front, like the teeth of a Rat or a Rabbit. The canines also protrude horizontally, and, being placed alongside of the incisors, are difficult to distinguish from the latter excepting that they are broader and thicker.

Of the pre-molars the anterior are canine-shaped, the median and posterior ones have three main, and one or two subordinate, cusps on the crowns. In both the upper and lower molars, cross-bridges stretch between the outer and inner front cusps as well as between the outer and inner hind cusps. There is an oblique ridge between the hind outer and the front inner cusp, and another is often present between the front outer cusp and the anterior "heel," producing, as Huxley has pointed out, almost a double crescentic pattern, as in many lower Mammals. The posterior molar has four or five cusps.

Of the milk-teeth, the incisors in the upper jaw change first. Of the molars, two are developed before the change of the pre-molars. In the lower jaw the incisors change first, and when two or three pre-molars have developed the last molar has still to come.

The arm-bone, or humerus, has one perforation (entepicondylar foramen) on its inner margin, and another above the joint (except in Perodicticus). The bones of the fore-arm (radius and ulna), and those of the leg (tibia and fibula) are not co-ossified (except in Tarsius), so that the palm or sole can be turned up at will.

The bones of the digits are more or less flat and rounded at the tips (differing in this respect from the Insectivora). One of the ankle-bones, for the articulation of the opposable great toe, the ento-cuneiform, as it is called, is rounded, as in the Anthropoid Apes and Man. The thumb is opposable, but its articulating bone in the wrist is not rounded, except in Avahis and Indris, which genera agree in this respect with Anthropopithecus and Man. The wrist has its central bone (os centrale) present; it is absent in Man and the higher Apes.

The knee is free and not united to the side of the body by integument.

The two halves of the lower jaw are not always co-ossified (as is the case in the Anthropoidea).

The opening in the base of the skull (the foramen rotundum) which transmits from the brain a branch of the fifth nerve for the upper jaw, and the sphenoidal fissure, which gives exit to the third, fourth and sixth cranial nerves, have but one aperture, as in the Rabbit, which belongs to the Rodentia.

The sacral vertebræ are generally three in number, and the lumbar and dorsal together vary from nineteen to twenty-three.

The brain, as Sir William Flower has observed, departs considerably from the form of what may be called the primatial type, and approaches in form to that of the carnivorous animals. The hind-brain, or cerebellum, is not completely covered by the cerebrum. The latter has but few convolutions (indicating a low intelligence), but its posterior lobe is always present, though more or less rudimentary, and so also are many fissures, which are characteristic of its surface in the higher Primates. The olfactory lobes are usually large and not covered by the cerebrum.

The uterus and structures for the nutrition of the young prior to birth are low in type, and approximate to the conditions seen in the Pig, the Horse, the Chevrotains, and the Ruminants. The unborn Lemur is often encased (as among the Sloths) in a skin-like covering (epitrichium) which breaks into patches before birth.

The tongue has a horny supplementary under-tongue (sublingua) attached beneath it. The stomach is simple, not formed of several compartments. The transverse portion of the great intestine is convoluted in a remarkable manner upon itself, the cæcum also being very large. The main arteries of the arm and leg break up (as in the Sloths) into an immense number of small vessels (called retia mirabilia) parallel to one another instead of being simple branching trunks.

The long tendons of the muscles for flexing the digits (the flexor longus digitorum) differ generally in arrangement from those of the higher Primates.

The Lemuroids are of no commercial value to Man.

As regards their distribution, the Lemuroidea are now absolutely confined to the Old World, and predominate in the island of Madagascar, where, as M. Grandidier remarks in his magnificent work on that country, there is scarcely a little wood in any district in which they are not found. Indeed, of the nearly seventy species of Mammals inhabiting that island, thirty-five, or one-half, are Lemurs. Members of the family also occur across the whole of the neighbouring continent of Africa, but their northern range does not reach quite to the tropic, whereas it extends some few degrees beyond it in the Southern Hemisphere. Elsewhere they are confined to the forests of the Oriental region. More or less isolated in Southern India, they re-appear in China, and spreading south to Java they reach as far east as Celebes and the Philippine Islands. The present isolation of the Lemurs in two such distant areas—in Africa and Madagascar and some of the Mascarene Islands on the one hand, and in Southern India, China, Ceylon, and the Malayan Islands on the other—has been considered by some naturalists as weighty evidence in favour of a former land connection between these distant regions.

Though so restricted in their distribution at the present day, this group was more widely represented in past ages of the world's history, as we shall have to point out later on. Abundant fossil remains prove that they lived in Europe and in North America, where to-day they are quite unknown.

The Lemuroidea are almost entirely arboreal, and seldom come to the ground, except the Sifakas, which then progress on their hind legs by a series of bounds, holding their hands over their head in a ludicrous fashion. Most of them are nocturnal, or crepuscular, sleeping the greater part of the day in holes or on a branch of a tree coiled up in a ball. Their food consists chiefly of leaves, fruits, honey, birds' eggs, and birds, or any small animals they can pounce upon.

The Lemurs now living are divided into three families. The Aye-Aye and the Tarsiers, on account of their very special characters, constitute each a distinct family—named Chiromyidæ and Tarsiidæ respectively—while the True Lemurs form the third, the Lemuridæ, to which all the remaining forms belong.

This very aberrant family contains only one species; the characters of the family and of the genus Chiromys are, therefore, necessarily those of the single species known.



Characters.—Head short and round; face short-snouted, with a patch of bristles below the eye, between the ear and the angle of the mouth; eyes round, prominent; eyebrows long and bristly; pupils wide, furnished with a false eyelid (a nictitating membrane); ears large, rounded, directed backwards, naked, and studded with small protuberances; tail longer than the body, bushy, with hair 3-4 inches long; hind-limbs longer than the fore-limbs, the thigh-bone being one third longer than the humerus, the hand the longest segment of the fore-limb; fingers long—the fourth the longest—with compressed and pointed claws, which are proportionately much longer than the toes; the middle or third digit slender and very remarkable, being extremely attenuated and wire-like; thumb opposable, and placed at an acute angle to the short index; great toe opposable, set at an open angle to the other digits, its nail flat; the remaining toes with pointed compressed claws (like the second toe of Lemuridæ and second and third of Tarsiidæ). Teats, two, placed low down on the abdomen. Length of body and tail together 36 inches. Skull highly arched, convex transversely; muzzle short and deep; bony palate not extending behind the middle of the posterior molar tooth; lower jaw with condyle elongated from before backwards and on a level with the cheek-teeth, its two halves united at an acute angle by elastic tissue, allowing each half to play independently of the other. Its dental formula, I $1⁄1$, C $0⁄0$, P $1⁄0$, M $3⁄3$ = 18. Incisors very large, curved, with persistent pulp, and enamel only in front, growing up as fast as worn away; canines absent (the last two characters as in the Rodents); long vacuity between incisors and pre-molar; pre-molar much smaller than molars; molars with flat crowns and very indistinct tubercules; milk-teeth agreeing more in number and form with those seen among Lemurs than with the permanent set; the upper jaw having its full set of two incisors, one canine, and a pre-molar tooth present; the lower jaw having one incisor, no canine, and one pre-molar tooth on each side. Dorsal and lumbar vertebræ together 18, sacral 3, and caudal 22-27.

Olfactory lobes of brain covered by the cerebrum; convolutions and grooves of cerebrum similar to those in normal Lemurs. Intestine 26 inches long; no striped tissue in the muscular sheath of the gullet at the anterior end of the stomach. Digastric muscle (for moving the jaws) very much developed in accordance with the great gnawing powers of the species.

Fur on back, flanks, tail, and limbs dark brown, nearly black, but with the white of the basal half of the hairs shining through; hair woolly at base; long hairs on top of head and back of neck tipped with white; short hairs of face dirty white. Nose and lips naked, flesh-coloured; ears black; sides of head and throat greyish-yellow; chest often bright yellow, the chin paler. Inner sides of limbs yellowish-white, and on the under surface of the body the basal part of hairs showing through, producing a pale yellowish-white, or sub-rufous, colour. Feet and digits black. Tail black, at its base greyish-white or greyish-brown, and often with long white hairs throughout. The species is more nearly related to the members of the genus Galago to be described later on, than to any other of the Lemuroidea.

Distribution.—The Aye-Aye is confined to the island of Madagascar. It makes its home in the dense parts of the great forest that runs along the eastern border of its central plateau, but only in that part of it which separates the Sihànaka Province from that of the Betsimisàraka, which is about 25 miles from the east coast, in latitude 17° 22′ S. It is more common than has been supposed, its noctural habits and the superstitious awe with which it is regarded accounting for its apparent rarity, and for the contradictory reports given of its habits.

Habits.—The Aye-Aye, whose name is derived from its call of "hai-hay," is one of the most singular of living animals. It was first discovered by Sonnerat during his travels in Madagascar in 1780, and by him sent to Paris. The skin remained unique in Europe for the best part of a century. Greatly owing to the superstitious dread in which the creature is held by the natives, it was for a long period, and is still, very difficult to procure, or to induce the natives to capture, specimens. Mr. Baron says that it is sometimes accidentally caught in traps by the natives, "but the owner of the trap, unless one of those versed in the Aye-Aye mysteries who know the charm by which to counteract its evil power, smears fat over it, thus securing its forgiveness and goodwill, and sets it free." In 1863 Dr. Sandwith sent a second example to Europe, the anatomy of whose body was made the subject of an exhaustive monograph by the late Sir Richard Owen. Since that date more than one specimen has been received alive, and its habits and constitution are now fairly well known. The Aye-Aye is entirely arboreal and nocturnal, sleeping during the day, with its body coiled round, lying on its side with its bushy tail spread over it as a covering. It suspends itself by its hind-limbs, and in this position it has been observed in captivity by Mr. Bartlett, using its hook-like finger to comb out its tail, to cleanse its face, the corners of its eyes, its nose, mouth, and ears, keeping meanwhile its other fingers closed. It lives in the depths of the forests, going about in pairs. Exquisitely keen of hearing, it can detect by sound the boring of insects within the dead branches of trees. Its attenuated wire-like finger acts as a probe to discover their position, and its powerful incisor teeth are used to cut down upon the tunnel of its prey, which consists principally of the Andraitra, the larva of a Beetle, which it then extracts with the same digit. The juices of plants are also supposed to form part of its food. It drinks after the manner of many Monkeys, by dipping its fingers into the water, and drawing them through its mouth. The Aye-Aye is fearless of Man, but in its wakeful hours, during the night, when irritated it can be very savage and strike out with its hands. The female produces but one young at a birth, and builds, in the fork of a tree, a ball-like nest, two feet in diameter, with an entrance hole in the side, forming it of the rolled up leaves of the Travellers'-tree, and lining it with small twigs and dry leaves. (Baron.)

This family, like the preceding, has been constituted for the reception of two animals which are so remarkably distinct from all the other species of Lemurs, as to necessitate their being thus segregated. Between these two forms however, so close a relationship exists, that they have often been considered as only varieties of the same species. The family, therefore, consists, as in the Chiromyidæ, of a single genus, the characters of which constitute also those of the family.

The Tarsiers are distinguished externally by the possession of a rounded head, and a very short, pointed muzzle; by their very large, long and naked ears, and eyes so remarkably large and protruding, as to form the most prominent feature of the face. The hind-limb, which is much longer than the fore-limb, is also very remarkable on account of the great elongation of the ankle-region (or tarsus) of the limb. The long and slender toes terminate in round, sucker-like discs, and are furnished with flat nails, except on the second and third toes, where the nails are merely compressed claws. The fore-limb, with or without the hand, is longer than the trunk; its digits also are long and slender (the third being longest, and the second equal to the fourth) and, like those of the foot, terminate in round sucker-like discs. Both the wrist and ankle are haired.

The long and Rat-like tail is longer than the body, and has a tufted termination. The skull presents enormous eye-cavities, the inner margins of the latter almost meeting in the centre. The orbits are nearly closed in from the temporal fossa by the union of the malar and alisphenoid bones—a character in which they differ from all other Lemurs, and approach the Anthropoid section of the Primates. Their dental formula is I $2⁄1$, C $1⁄1$, P $3⁄3$, M $3⁄3$ = 34. Of the upper jaw, the incisors are prominent and unequal, the anterior ones being larger than the posterior, and in contact in the middle line, thus leaving no central gap in the front of the jaw, as is the rule among Lemurs; the canines are about as long vertically as the inner incisor, and are smaller than the corresponding tooth in the True Lemurs; the pre-molars are canine-like, sharp, pointed, and furnished with a cingulum; the anterior pre-molar is smaller than the two others; the posterior pre-molar has one external and one internal cusp; the molars, all nearly equal in size, are wide transversely, strongly cingulate, and have two prominent external cusps. In the lower jaw, the solitary incisor in each half is small, and, instead of protruding horizontally, is nearly erect; the canines are also almost erect, and less like incisors than is usual in the Sub-order. The pre-molars are sharp, but the anterior is smaller than the two posterior; the anterior and median molars have four cusps, and are cingulate, while the posterior molar has five cusps.

The Tarsiers have nineteen dorsal and lumbar vertebræ together, and twenty-seven in the tail. The humerus presents a perforation (the entepicondylar foramen) at its lower inner side, and another nearly in the centre above the hinge. The femur is more than twice the length of the arm-bone; the lower half of the slender fibula is co-ossified with the tibia, while two of the tarsal, or ankle-bones (the calcaneum and naviculare), are remarkably elongated, thus giving to the hind-limb of these animals the singular conformation from which they derive their name. The large intestine is not convoluted upon itself as in so many of the Lemurs, nor is there a cæcum at the junction of its smaller and larger portions.

Characters.—On the upper lip, sides of nostrils, and over the eyes long, delicate black hairs (vibrissæ); hair on nose very short, longer in front of ears and at angles of mouth. Fur of body generally thick, woolly, the basal two thirds slate-grey, the terminal third brownish-yellow. Face to forehead fawn-brown, somewhat darker around and between the enormous liquid brown eyes. Top and back of head and shoulders of a more uniform and darker shade; rest of back apparently mottled, owing to the light-tipped hairs of that region gathering into locks. Under side of body, inside of arms and legs paler. Tail darker brown, rufous at base of upper side. Size not exceeding that of a small Rat.



Distribution.—Found only in the jungles of the Malayan islands of Sumatra, Java, Banka, Billiton, and Borneo.

Characters.—Closely related to the preceding species in size and other characters, but distinguished by the colour of the hands, which are dark brown.

Distribution.—Inhabits the islands of the Indian Archipelago, farther to the eastward than those in which Tarsius Tarsius is found. It has been recorded from Celebes, and the neighbouring groups of Salayer and Sanghir, and from some of the Philippine Islands, such as Bohol and Mindanao.

Habits.—The habits of both species of Tarsier are identical, and may be described together. They are almost entirely nocturnal and arboreal animals, rarely, of their own accord, coming to the ground. They move from place to place by leaping along the larger branches, or from tree to tree, even when these stand several feet distant. When they do descend, however, they advance on the ground by the same curious Frog-like leaps, without bringing their fore-limbs down to the ground. The Tarsier is said to climb easily, even without grasping, by means of the round discs on its slender finger-tips, which, like suckers, enable it to hold on by the side pressure of its limbs to any smooth surface, such as the stems of the bamboo-brakes which it frequents. Mr. Charles Hose, in his "Mammals of Borneo," states that, in that island, the Tarsier is found in the jungles of the low country, skipping about from branch to branch. According to the notes of this excellent field-naturalist, it has a habit of turning its head almost completely round without moving the rest of its body. This very remarkable creature lives in pairs in the tropical forests, in holes in the tree stems, or under their roots, feeding chiefly on insects and small lizards, which, as Mr. Cuming has recorded, it holds by its fore-paws while devouring, sitting up the while on its posterior. In drinking it is also said to lap water like a Cat. The Tarsier seldom makes any kind of noise, but when it does emit a sound, it is a sharp, shrill call. The female produces one, rarely two, young at a birth; these are similar to the parents. They are covered with hair, and have the eyes open. Mr. Hose further states that the mother often carries her young one about in her mouth, after the manner of a Cat. On the second day after its birth, the infant Tarsier can move about by itself. By the natives of Sumatra, and, indeed, of most of the islands inhabited by these animals, the Tarsiers are held in superstitious dread, their presence in the neighbourhood of the rice-fields being supposed to portend misfortune to the owner or to some member of his family.

Their elongated ankle-bones, and their leaping habits, seem to indicate that the Galagos and the Chirogales, or Mouse-Lemurs, are the nearest relatives of the Tarsiers.